> Then again in July the same year, another runaway gas well in Ukraine was sealed with a 3.8 kiloton nuclear explosion at a depth of more than 2.4 km.

This is not true.

https://uk.wikipedia.org/wiki/%D0%A4%D0%B0%D0%BA%D0%B5%D0%BB...

> Експеримент не мав успіху: закрити викид за допомогою вибуху не вдалося. Газовий факел згасили через кілька місяців стандартними методами.

> The experiment was not successful: the runaway was not sealed with the explosion. Gas flare was exhausted with standard methods a few months after.

I guess at those depths ground water contamination wasn't really a problem